#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main()
{
	int start = 2;
	int n = 0;
	int sum = 0;
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
	{
		sum += start;
		start += 3;
	}
	printf("%d", sum);
	return 0;
}